In a study published in the scientific journal PLOS ONE, UH Manoa researchers in the College of Tropical Agriculture and Human Resources compared the historical and modern-day distributions of a native Hawaiian leafroller moth, tracking its steep decline and exploring possible causes for this decline.

The moth, Omiodes continuatalis, used to be one of the most common native moths in Hawaii during the early 1900s, when it was widespread across all the main Hawaiian Islands. Over the last century, however, populations have declined dramatically. The moth is now extinct on Oahu and Kauai but is still found from Molokai to the Big Island. Introduced and invasive insects such as ants and parasitic wasps, which attack the caterpillar stage, have been blamed for the declines of this species and many other native caterpillars.

The research was part of a broader study conducted by Dr. Adam Vorsino, Cynthia King, Dr. William Haines and Dr. Daniel Rubinoff of the College of Tropical Agriculture and Human Resources, and was funded by the USDA to assess the impacts of historical biological control efforts on native insects.

The scientists compiled data from museum specimens from historical (pre-1970) and recent (post-2004) time periods, and produced maps of the moth’s ideal habitat in both time periods, based on climate, elevation, vegetation and the records of moth occurrence over the decades. They found that the moth’s habitat has declined dramatically, with only about 2% of high-quality habitat remaining.

The scientists also modeled future distributions of the moth based on predicted changes in climate, and concluded that climate change was not the likely cause of the declines. Additionally, because caterpillars of the moth can feed on many native and non-native grasses, including common pasture grasses and roadside weeds, food resources are not likely to be a limiting factor for this species. The declines are more likely correlated with the impacts of non-native parasitic wasps and other predaceous insects.

Because the study mapped the best habitat for the moth on all the islands, based on climate and vegetation, it identified areas where populations of the moth are most likely to remain, even on islands where it is currently thought to be extinct. Scientists recommended that surveys be conducted in these areas to attempt to rediscover populations of the moth. These sites may also be promising sites for re-introduction of the moth within its former range.

The article may be found at PLOS ONE online at: http://dx.plos.org/10.1371/journal.pone.0051885